1. Field of the Invention
The invention relates to a liquid crystal display. Particularly, the invention relates to a liquid crystal display having a good color saturation.
2. Description of Related Art
Since a liquid crystal display (LCD) has advantages of small size, high image quality, low power consumption, and no irradiation, etc., it replaces a conventional cathode ray tube (CRT) display and becomes popular in the display market. However, compared to the CRT display, the LCD generally requires a backlight source for displaying images. The backlight source used by the LCD includes a cold-cathode fluorescent lamp (CCFL) backlight source and a light emitting diode (LED) backlight source.
Since a white LED has advantages of low heat generation, low power consumption, long service life, fast response time, small size, and suitable for planar package, etc., it is regarded as “white illumination revolution”. In aspect of an application market, the white LED is gradually applied in backlight modules of portable display devices and televisions due to its advantages of low power consumption, small size and fast response time, etc. However, a commonly used white LED generally uses a blue LED chip in collaboration with yttrium aluminium garnet (YAG), although it has advantages of easy package and small size, it is inadequate in performance of color saturation. Moreover, since the white LED is a dot light source, a plurality of optical films (for example, diffusion films, light-guiding plates and enhancement films, etc.) has to be used to achieve an even planar light source, so that it is hard to reduce a whole thickness and a fabrication cost of the backlight source.
In recent years, some developers developed a concept of using organic electroluminescent devices to serve as backlight sources, so as to reduce utilization of the optical films. FIG. 1 is a schematic diagram illustrating spectrums of two organic electroluminescent devices OLED-1 and OLED-2 developed by an Eastman Kodak Company, and FIG. 2 is a CIE 1931 chromaticity diagram of a LCD using the organic electroluminescent devices OLED-1 and OLED-2 as backlight sources.
When the organic electroluminescent devices OLED-1 and OLED-2 of the Eastman Kodak Company are used as the backlight sources, color coordinates (x, y) and luminance (Y) of red color, green color, blue color and white color displayed by the LCD are listed in a following table. Moreover, color saturations (NTSC %) of the LCD are also listed in the following table.
RxRyRYGxGyGYBxByBYWxWyWYNTSCPatent OLED10.6390.3375.290.2500.58014.770.1390.0643.220.2550.2547.7672.1%Patent OLED20.6460.3437.560.2590.54413.270.1200.1122.990.3250.3267.9461.7%
According to the above table, it is known that when the organic electroluminescent devices OLED-1 and OLED-2 of the Eastman Kodak Company are used as the backlight sources, the color coordinates of the white colors displayed by the LCD are respectively (0.255, 0.254) and (0.325, 0.326), which are obviously different to the color coordinates (0.28, 0.29) of the white color displayed by a general television product. Moreover, when the organic electroluminescent devices OLED-1 and OLED-2 of the Eastman Kodak Company are used as the backlight sources, the color saturations (NTSC %) of the LCD are only 72.1% and 61.7% (shown in FIG. 2). Obviously, when the organic electroluminescent devices OLED-1 and OLED-2 of the Eastman Kodak Company are used as the backlight sources, problems of poor color saturations and undesired color coordinates of the white color are occurred.